Television scanning system



Apnl 20, 1954 G. c. szlKLAl 2,676,200

TELE/VISION SCANNING SYSTEM Filed Nov. 9, 1950' y 2 Sheets-Sheet l April2o, 1954 Filed Nov. 9, 1950 G. c. szlKLAl 2,676,200

TELEVISION SCANNING SYSTEM 2 sheets-sheet 2 L//VE Patented Apr. 20, 1954UNITED STATES ATENT OFFICE TELEVISION SCANNING SYSTEM of DelawareApplication November 9, 1950, Serial No. 194,795

This invention relates to the art of television and particularly totelevision scanning systems.

In accordance with the present standards for black and white television,each picture frame consists of 525 horizontal lines. In operation,however, the vertical resolution of the pictures is comparable to onlyabout 70% of the theoretical resolution which might be expected. Afterdeducting blanking time, the practically realizable resolution,according to the present standards is approximately equivalent to 335horizontal lines. This is the well-known Kell effect. A paper on thissubject was published in the Proceedings of the I. R. E. of November1945. This paper is titled An Experimental Television System-TheTransmitter by R.. D. Kell, A. V. Bedford and M. A. Trainer,Accordingly, full advantage of the 525 lines is not realized.

The horizontal resolution of the television image may be materiallyimproved by the utilization of the dot interlacing principle prop-osedfor color television. One such color system forms the subject matter ofa copending U. S. applica- Claims. Cl. 178-5.4)

tion of R. C. Ballard, Ser. No. 117,528 filed September 24, 1949 andtitled Systems of Color Television. The dot interlace principle inaccordance with the Ballard case is primarily for use in colortelevision systems. The image is formed by a multiplicity of dots in thecomponent image colors. The dots `are displayed upon the screen in acertain sequence. However, in successive fields, the dots of any onecolor are interlaced horizontally, thereby materially improving thehorizontal resolution of the image.

It is desirable, therefore, to provide a system for increasing thevertical resolution of the reproduced image so that a greaterutilization may be made of the 525 horizontal lines of the scannedraster.

It is an object of the present invention, therefore, to provide animproved scanning system for television by which to increase thevertical resolution of the reproduced image.

Another object of the invention is toprovide zontal scanning is effectedin undulating scanning traces instead of the conventional linear traces.The horizontal scanning, in general, is of a type disclosed in U. S.Patent 2,222,934, granted November 26, 1949 to A. D. Blumlein and titled"Television Transmitting and Receiving System. In the Blumlein system,the undulating traces of all of the horizontal lines of the raster arein phase with one another. The present invention provides for a phaseshift in the undulating traces of successive fields. In this Way, thehorizontal resolution of the reproduced image is fully equal to thatproduced by the conventional straight line scanning. The 180 phase shiftof the undulating traces of successive elds is produced in a systemoperating in accordance with the present standards by employing afrequency for the undulations, which may be a sinusoidal oscillation,that is an odd multiple of one-half of the horizontal scanningfrequency.

The novel features that are considered characteristic of this invention,are set forth with particularity in the appended claims. The invention,itself, however, both as to its organization and method of operation, aswell as additional objects and advantages thereof, will best beunderstood from the following description when read in connection withthe accompanying drawings.

In the drawings:

Figure 1 is a block diagram of television transmitting apparatusembodying the present invention;

Figure 2 is a block diagram of television receiving apparatus embodyingthe invention;

Figure 3 is a graphical representation of the manner in which thepresent invention operates to increase the vertical resolution of thepicture;

and,

Figure 4 is a graphical illustration of the use of the invention in acolor television system.

Reference rst will be made to Figure l. Light from an object Il isprojected by an optical's'ystem l2 onto the photosensitive cathode I3 ofa television camera tube I4. The camerajtube, as illustrativelydisclosed herein, may be an image orthicon. It will be clear to thoseskilled in the art that other types of camera tubes may be employed inthe practice of this invention with substantially equal facility.

. The camera tube is provided with the usual deflection system whichincludes horizontal and vertical deflection coils l5 and I6,respectively. In addition, the tube is provided with an auxiliarydeflection coil Il which is effective to produce a vertical oscillationof the electron beam which is used to scan the target electrode I8.

Video signals are derived from the output electrode I9 of the cameratube I4 and are impressed upon a video signal amplifier 2|. The ampliedvideo signals derived from the amplier 2l are impressed upon atransmitter 22, the output of which is connected to excite a radiatingantenna 23. It will be understood that the transmitter 22 may beconventional and includes apparatus for mixing the video signals withthe synchronizing signals and for modulating a carrier wave forradiation.

The transmitting apparatus also includes a horizontal deflectiongenerator 24 which is coupled to the horizontal deection coil l forexcitation thereof. Similarly, a vertical deflection generator 25 isprovided and` is coupled to excite the vertical deflection coil i8.Further in accordance with the present invention, there is provided anauxiliary deflection generator 25 which is coupled to the auxiliarydeilecting coil H.

The deflection generators 2d, 25 and 26 are controlled by asynchronizing signal generator 21 so that the waves developed by therespective deflection generators are maintained in proper relationshipto one another. Also, the synchronizing signal generator 2'! is coupledto the transmitter 22 to supply the synchronizing signals forcombination with the video signals to form a composite television systemin the usual manner.

The general operation of the transmitting apparatus of Figure 1 Will bedescribed briefly before considering the receiving apparatus andpresenting a more detailed description of the over-all operation of thesystem in accordance With this invention. For the purpose ofconcreteness rather than restriction, the operation of the apparatuswill be described with reference to certain deflection frequencies. Thehorizontal deflection generator 24, for example, will be assumed todevelop a substantially saw-tooth Wave at a frequency of 15,750 cyclesper second. Similarly, the Vertical deflection generator 25 will beassumed to develop another saw-tooth Wave having a frequency of 60cycles per second. These frequencies are, in accordance with the presentstandards, those at which the line and field scanning operations areeffected. Also, it will be understood that the apparatus operates inaccordance with the present established standards for black and whitetelevision, whereby 30 complete frames of a 525 line picture are scannedper second. Each frame consists of two fields of interlaced horizontallines.

In accordance with the present invention the auxiliary deflectiongenerator 26 will be assumed to develop a substantially sinusoidal Wavehaving a frequency of 3,583,125 cycles per second. It will be seen thatthis frequency is the 455th harmonic of one-half of the horizontalscanning frequency. It, therefore, satisfies the requirement inaccordance with this invention that the auxiliary vertical deflection beeffected at a frequency which is an odd multiple of onehalf thehorizontal scanning frequency. It will be understood that the frequencyat which the auxiliary deflection generator 26 is assumed to operate ismerely illustrative of the operation of this invention. Obviously, otherfrequencies may be employed Without departing from the inventionprovided that they meet the requirements specified. The form of theauxiliary deflection wave need not be sinusoidal as assumed.

Other wave shapes, such as rectangular or square ones, may beu sedWithin the scope of this invention.

Also, in accordance with this invention, the magnitude of the auxiliarydeflection wave derived from the generator 26 should be such that thesinusoidal vertical deection of the scanning beam has an amplitude whichis substantially equal to one-half of the normal spacing betweenadjacent horizontal lines of the raster.

Before considering in any greater detail the operation of the system inaccordance with this invention, reference Will be made to Figure 2 for adescription of the receiving apparatus. An antenna 28, of a kind tointercept the radiated carrier wave, is coupled to a receiver 29.. Itwill be understood that the receiver may be entirely conventional,comprising the usual carrier wave-amplifying and signal-detectingapparatus.

Accordingly, it will be understood that there may be derived from thereceiver 29 the video signals which are impressed upon a video signalamplifier 3|. Also, the receiver 29 may be coupled to a synchronizingsignal separator 32 by which to recover the synchronizing signals fromthe received composite signal to the exclusion. of the video signalcomponent.

The video and synchronizing signals are employed to operate animage-reproducing device such as a cathode ray tube or kinescope 33. Thevideo signals derived from the amplier 3| are impressed upon anelectrode of the electron gun, with which the kinescope 33 is provided,so as to modulate the intensity of the electron beam in accordance withthe video signal information. The kinescope 33 also is provided withhorizontal and vertical deflecting coils 34 and 35, respectively. Tnaddition, in accordance with the present invention, the kinescope isprovided with an auxiliary deflecting coil 36 by which to produce a highfrequency Vertical deflection of the electron beam.

The receiving apparatus also includes a horizontal deflection generator3l' adapted to produce a substantially saw-tooth Wave at the horizontalscanning frequency of 15,570 cycles per second. The horizontaldeflection generator is coupled to energize the horizontal deflectingcoil 34. A vertical deflection generator 38 is adapted to generate asubstantially saw-tooth wave at the field scanning frequency of 60cycles per second and is coupled for energization of the verticaldcecting coil 35. Finally, an auxiliary deflection generator 39 capableof developing a substantially sinusoidal Wave at a frequency of3,583,125 cycles per second is provided for exciting the auxiliarydeilecting coil 36. The deiiec tion generators 3l, 38 and 39 are coupledto the synchronizing signal separator 32 for control in the usualmanner.

The receiving apparatus of Figure 2 operates in a manner substantiallysimilar to the previously described transmitting apparatus of Figure 1.Horizontal and vertical deflection of the video signal-modulatedelectron beam by the coils 3 and 35, respectively is conventionallyeffected. In addition, the horizontal traces made by the electron beam,in scanning the luminescent screen of the kinescope 33, have asinusoidal form produced under the influence of the auxiliary deflectingcoil 36. In this way, the scanning operations at the transmitter and atthe receiver are made identical.

For a more detailed consideration of the manner in which the presentinvention operates to i i i increase the vertical resolution of thetelevision image, reference now will be made to Figure 3. This figureconsists of sinusoidal curves `il and d2 representing, respectively, theauxiliary vertical deflections of the scanning beams. These curves mayalso be considered to represent the two different types of traces madeby the electron beams on the target electrode IS and the luminescentscreen 4i), respectively, of the camera tube Ii and of the kinescope 33.The curve li! represents the scanning pattern for each of the horizontallines of the raster in elds i, 5, 8, etc. The curve 42 represents thescanning pattern for each of the horizontal lines of the raster infields 2, 3, B, l, etc. t will be noted that the curves 4l and 42 are180 out of phase with one another. It may be seen that, in eachhorizontal line of the raster, the sinsuoidal curves fil and 42 have anodd nmnber of half cycles.

In accordance with the presently assumed frequencies, each trace such asrepresented by the curves 5I and i2 includes 227.5 cycles per horizontalline. Consequently, after scanning an odd number of lines the curves diand l2 will have an odd number of half cycles. This has the effeet thatthe sinsuoidal traces representing the horizontal lines of the rasterwill have completed an odd number of half cycles at the completion ofscanning a raster of 525 lines, in accordance with the presentstandards. Therefore, in the second scansion of the lirst line of theraster, the horizontal trace will be 180 out of phase with thehorizontal trace of the initial scansion of this line. It is clear thatthe sinusoidal scansion of all of the remaining lines of the raster alsowill be 180 out of phase with the iirst scansion of these lines.

By such a process, it will be seen that each elemental image of the areain eiiect is divided into upper and lower halves. This has the ci fectof increasing the vertical resolution of the image substantially by afactor of 2. It is true that, in such a situation, the repetition rateof each spot of the image is equal substantially to one-half of thatproduced by the more conven tional straight line scanning. However, itmust be taken into account that these spots or areas are very small,being of the order of magnitude of one-half of the conventionally sizedareas in straight line scanning. Therefore', because of the increaseddegree of neness of the image areas, the lower repetition rate producedin accordance with this invention will not prodluce objectionableflicker.

The chart portion of Figure 3 is intended to represent a raster of atelevision image separated into horizontal lines and elemental areas.The raster contains an odd number of horizontal lines which, asillustrated, is 5 in the present instance. By this means, an analogycomparable to an actual television raster of 525 lines may be made. Notonly does the actual television raster con tain an odd number of lines,but the number of lines is equal to 4 N+1. In the actual case, N isequal to 131. In the assumed case illustrated in Figure 3, N is equalto 1. It is not intended to imply that the present invention isapplicable only to those television systems having rasters containing anumber of lines equal to 4 N+1. On the contrary, it is equallyapplicable to any system having an odd number of scanning lines. Theonly diierence between the system disclosed and any other system having`an odd number of scanning lines is in the particular pattern in whichthe elemental areas of the complete image is scanned.

In the simulated raster of Figure 3, each of the ve horizontal lines isassumed to contain nine elemental areas. Further, each of the elementalareas is assumed to be sub-divided into upper and lower portions. Inaccordance with this invention, the scanning of each of the elementalareas of the raster is ei'ected by scanning only a half of each of theareas at a time. It will be noted that the horizontal arrangement of theraster areas is related to the sinusoidal curves lil and 42 in such aWay that each area is in alignment with a half cycle of the curves IHand i2. Furthermore, for the purpose of this description, it will be.assumed that the position of the half cycles of the curves 4I and 42above or below the of the curves corresponds to the scanning of theupper or lower halves of the image areas.

The chart has numbers 1, 2, 3 and 4 in the upper and lower halves ofeach of the raster areas. These numbers correspond to the successivescanning Ii'elds. The numbers indicate those portions of the elementalarea which are scanned during the different fields. Furthermore, it isassumed that the scanning of the raster is in accordance with thepresent standards and employs a two-to-one line interlace. Therefore,the odd numbered lines such as I, III and V are assumed to be scanned insuccession in one field, while the even numbered lines such as Il and IVare scanned in succession during the next eld.

Without going through the complete chart in detail, starting with theupper half of the elemental area of line I, the scanning trace acrossthis line is in accordance with the curve il. Accordingly, the upperhalves of the rst, third, fifth, seventh and ninth elements are scannedduring eld 1. Also during field l, the lower halves of the second,iorurth, sixth and eighth areas are scanned. In each of. these halves ofthe elemental areas of line I, the numeral 1 appears, indicatingscansion of this period during field 1. It will be noted that the upperhalf of the ninth elemental area of line V is the last portion of theraster scanned during eld l. Therefore, the lower half of the first areaof line II is the nrst portion of the raster scanned during field 2. Thescanning pattern, in accordance with the present invention, is of such acharacter that the upper half of the ninth elemental area of line IV isthe last portion of the raster scanned during field 2. At this pointone-half of each elemental area of the entire raster has been scannedonce.

The entire raster again is scanned in two interlaced fields insinusoidal traces so that the other halves of the elemental areas alsoare scanned. Inasmuch as it was the upper half of the ninth element ofline IV which was scanned during eld 1, the rst area to be scanned infleld'B is the lower half of the .first area of line I. Now, it is seenthat the sinusoidal scansion of line I is in accordance with the curvei2 and is 180 out of phase with the first scansion of this line. Thesame relationship exists for the scansion of the even-numbered linesduring field 4 so that, at the completion of neld 4, the entire area ofthe raster has been covered. Furthermore, it is seen that, at thecompletion of the scansion of field 4, the pattern is such that it willrepeat in iield 5 in the manner indicated for eld 1.

The present invention is not necessarily limited for use in black andwhite television systems.

^ rOnxthelcontrary, it may berusedtof-considerable V@vision system iscovered in a copending U. S.

application of John Evans, Serial No. 111,384 filed August 20, 1949 andtitled Color Television. In such a color television system a videosignal V.Wave has successive instantaneous amplitudes representative ofthe component color'light intensities of differentelemental areas of animage. This Wave is sampled at a relatively high fref yquency to deriveindividual color-representative video signal pulses by which toreproduce the f image.

It is in this type of system especially, that the horizontal dotinterlacing technique, forming the subject matter of the Ballardapplication previously referred to, is particularly useful.` .Accordingto theEallard technique thesignal sampling is'eiected at a frequencywhich is an odd mul- `-tiple of one-half of the line scanning frequency.By this means alternate ones of the horizontal Adots are produced inone, scansion ofv each ofthe lines and the intermediate dots areproduced in the next scansion of these lines.

. The operation of a dot multiplex color televif Ysion system may befurther enhanced by the use of the present invention.. Thel vertical dotinterlacing, as produced by the operation of thepresent system, willhave little orno 'effect upon I those portions of the image inwhchhighchroma ,colors are present. It .will produce', however, `benecialresults in a dot multiplex color television system in those areas of thepicture which 'are black and white, different shades of gray and evenlow chroma'colors.

The manner in whichthis' benecial result is produced is illustratedgraphicallyl in Figure l to which reference v now will be made. It isassumed that the image to be reproduced con- I sists of a vertical greenbar forming-the 'left-hand. portion thereof and a black and white orgray bar formingthe right-hand portion. Only the .first two lines of theraster are indicated for the reason that, in view of the foregoingdescription Vgiven in connection with Figure 3, it is believed thatthose skilled in the art will understand the manner in which thescanning system in accord-v during the scanning process inaccordancewith this invention. The intensity of the light pro- -duced on thescreen by theset dots is determined zfby the intensity modulation of theelectron beam. inthe usual manner.

Consider first the left-hand or green portion of the image area duringthe scanning of field 1. During each positive half cycle of thetracef43, the intensity` of the electron beam is modulated toproduce.visible light which is representative of the green area of the picture.During the z negative half cycles of'the 'trace 43,'there isno intensitymodulation of the electron beam to represent the green colorinformation. Instead, in accordance with the dot multiplex principle asdisclosed inthe copending EvansapplicationA referred to, the othercomponent colors; such as red and blue, of the image are displayed inthe intervals between the green display. Accordingly, it is seen that,during the scansicn of line I of the raster, during eld 1,green-representative areas such as lil are excited.

Also, during the scansion of line I during eld 1 in the black and Whiteportion of the picture area, the electron beam is modulated in intensityto represent the black and white or low chroma portion of the picture.In the case of a black and White representation, for example, it is seenthat the screen is excited to produce light during all positive halfcycles of the trace i3 t0 produce luminous areas such as 48. Now,however, because the intensity of the beam is modulated in accordancewith the black and white picture information, all of the component.image colors may be considered to be present in equal intensity sinceit is assumed that this color television system is of the additive type.Accordingly, the beam is modulated in accordance with the black andwhite information substantially continuously with the result that thereare produced, during the negative half cycles of the trace 43, luminousareas such as i9.

As more fully described in connection .with Figure 3 and with additionalreference to the immediately foregoing description of Figure 4., it willbe appreciated that, While raster line Il is being scanned during eld 2,the electron beam intensity is modulated tof represent the green picturearea. Accordingly, there are produced green luminous dots or elementalareas such as 5I during positive half cycles of the trace fil/. In asimilar manner, the blaclrrand white, or low chroma color portion of thepicture is represented by the areas 52 and 53 produced during positiveand negative half cycles respectively of the trace 44.

During the scansion of raster line I during held 3, thev intensitymodulation of the electron beam, as itA follows the path represented bythe trace 45 across the green portion ofthe picture. produces greenluminous dots such'as 54. It is noted that these green areas appearmidway Ybetween the green areas such as 4? produced in the rst scansionof this line. This is the result produced by the horizontal dotinterlacing system as covered in the previously referred to copendingBallard application. Again, it is noted that no green areas are producedduring the negative half cycles of the `trace 45.

Further scansion of raster line I during eld 3 produces black and whitepicture elemental areas such as' 55 and 56. These areas are produced,

' respectively, during positive and negative half cycles of the trace43. It is seen, in the right- `hand portion of'Figure 4, that the dotinterlacing principle is employed to produce the same beneficial resultsas in the color portion of the picture. Furthermore, it maybe seen thatan eiective vertical interlacing ofthe black and Y Y i seen that thevertical resolution in the low chroma color and/or black and white areasof a picture is substantially two times that of the present black andwhite systems.

It, therefore, may be seen from the foregoing description of anillustrative embodiment of the invention that there is provided animproved scanning system for television purposes by which the verticalresolution of the reproduced image may be substantially increased.Furthermore, it may be seen that this increase in vertical resolutionmay be secured Without increasing the frequency bandwith requirements ofthe signal transmission channel. Moreover, the present system isentirely compatible with present black and white television systems. Inorder to realize the full benefit of the invention, it is necessary, ofcourse, that the scanning system be employed both in the transmitter andin the receiver. Nevertheless, it is not necessary that every receiverbe provided with a scanning system in accordance with the invention,even though the transmitter does operate in such a manner. A receiver inwhich linear scanning is effected will operate entirely satisfactorilywithout, however, the advantage of the additional benefits in verticalresolution to be derived from the use of the invention both at thetransmitter and at the receiver.

The nature of the invention may be ascertained from the foregoingdescription oi' an illustrative embodiment thereof. The scope of theinvention is set forth in the following claims.

What is claimed is:

1. A system for scanningl a television raster comprising, meansincluding a horizontal defiection system for effecting a horizontalscanning of said raster, means including a vertical deection system foreffecting a vertical scanning of said raster, said raster having an oddnumber of substantially horizontal lines appearing in a plurality ofline-interlaced fields, means including an auxiliary vertical deilectionsystem for effecting an undulating horizontal scanning of said raster,and means controlling said auxiliary deflection system to effect a 180phase shift between successive scansione of the same line in dierentones of said fields.

2. A television scanning system as defined in claim 1 wherein, saidauxiliary deflection system controlling means is of a character toproduce a wave having a frequency related to the frequency of saidhorizontal scanning in such a way that said 180 phase shift ofsuccessive scansions of the lines of said raster is automaticallyeffected.

3. A television scanning system as defined in claim 1 wherein, saidauxiliary deflection system controlling means is of a character toproduce a wave having a relatively high frequency equal to an oddmultiple of one-half the frequency of said horizontal scanning.

4. A television scanning system as defined in claim 1 wherein, saidauxiliary deflection system controlling means is of a character toproduce a wave by which to effect said undulating scanning in anamplitude equal substantially to 10 one-half of the normal spacingbetween adjacent horizontal lines of said raster.

5. A television scanning system as defined in claim 1 wherein, saidauxiliary deection system controlling means is of a character to producea wave by which to effect said undulating horizontal scanning in asubstantially sinusoidal manner.

6. A television scanning system as defined in claim 1 wherein, saidhorizontal and vertical deflection systems are so related in frequencyto one another that said raster consists of two interlaced elds and saidraster is completely scanned in four of said fields.

7. A system for scanning a television raster comprising, means includinga horizontal deection system for eecting a horizontal scanning of saidraster, means including a vertical deection system for effecting avertical scanning of said raster, said horizontal and verticaldeflection systems producing a raster having an odd number ofsubstantially horizontal lines appearing in a plurality of interlacedfields, means including an auxiliary vertical deflection system foreffecting an undulating horizontal scanning of said raster, and meanscontrolling said auxiliary deection system so as to effect saidundulating scanning at a relatively high frequency equal to an oddmultiple of one-half of the frequency of said horizontal scanning.

8. In a color television system in which successive instantaneousamplitudes of a video signal wave represent the component color lightintensities of different elemental areas of an image, means fordeflecting an electron beam horizontally and vertically to scan a rasterhaving an odd number of substantially horizontal lines appearing in aplurality of line-interlaced elds, means for sampling said video signalwave at a relatively high frequency equal to an odd multiple of one-halfof said horizontal beam deflection frequency and means for effecting anauxiliary vertical deflection of said beam at a relatively highfrequency equal to an odd multiple of one-half of said horizontal beamdeflection frequency to produce undulating horizontal raster lines.

9. Color television apparatus as dened in claim 8 wherein, said videosignal wave-sampling means for each of said component image colors andsaid auxiliary vertical beam deflection means operate at the samefrequency.

10. Color television apparatus as defined in claim 8 wherein, said videosignal wave represents a, number of component image colors, and saidvideo signal wave-sampling means for all of said component colorsoperates at a frequency which is equal to an odd multiple of saidauxiliary vertical beam deflection frequency.

References Cited in the ille 0f this patent UNITED STATES PATENTS NumberName Date 2,222,934 Blumlein Nov. 26, 1940 2,431,115 Goldsmith Nov. 18,1947 2,508,267 Kasperowicz May 16, 1950

